t = -2:0.01:2; T = [15,25,51,101]; for k = 1:length(T) a=0; for n = 1:2:T(k) b=exp(1i*n*pi*t)/n; a=a+b; end y=2*a/(1j*pi); x=0.5*square(pi*t); figure; p=plot(t,real(y),t,x); axis([-2,2,-0.8,0.8]); set(gca,'XTick',-2:1:2) set(gca,'YTick',-0.8:0.4:0.8) set(gca,'XTickLabel',{'-2','-1','0','1','2'}) set(gca,'YTickLabel',{'-0.8','-0.4','0','0.4','0.8'}) xlabel('自变量') ylabel('函数值') titlemsg=sprintf('吉布斯现象N=%d的合成波形',T(k)); title(titlemsg) text(0,-0.5,'\leftarrow 方波函数','HorizontalAlignment','left') set(gcf,'Color','w') hold on end

Null is a term that represents the absence of a value or data in a database or programming language. It can be used to denote a missing or undefined value, empty space, or an unknown value. In programming languages, null is often used to indicate an uninitialized variable or a pointer that does not point to any valid memory address. In databases, null is used to represent a missing or unknown value in a field.